Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Pivalic acid synthesis

A cntical component of this effort was an extensive investigation of the classical Paal-Knorr pyrrole synthesis" that finally resulted in a successful cyclodehydration in a model system when a full equivalent of pivalic acid was used as catalyst (Scheme 4). Thus condensation of commercially available isobutyrylacetanilide 18 with benzaldehyde in the presence of p-alanine and acetic acid afforded the enone 19 in 85% yield. [Pg.119]

Treatment of this enone with 4-fluorobenzaldehyde under the conditions of Stetter, utilizing A -cthylthiazolium catalyst 20 under anhydrous conditions produced the highly substituted 1,4-diketone 21 in 80% yield. Treatment of diketone 21 with the diethyl acetal of 3-amino-propanal under the carefully controlled conditions described above (1 equivalent of pivalic acid) afforded penta-substitued pyrrole 22 in 43% yield and, very significantly, demonstrated that a totally convergent synthesis was possible. With this result in hand, it became possible to envision a route in which a fully elaborated side-chain could be combined with the appropriate 1,4-diketone (i.e. 21), to assemble the entire molecule in one operation. [Pg.120]

The Z-protected derivative, again prepared by standard methods using benzyl chloroformate,t208 may serve in the case of racemic pipecolic acid for resolution into the pure enantiomers by fractional crystallization with L-tyrosine hydrazide/208 Acylation with N-protected pipecolic acid or of pipecolyl peptides is performed by standard procedures via the active ester methods, e.g. A-hydroxysuccinimide ester/121 by the mixed anhydride method, e.g. with isobutyl chloro-formate 95-114 or pivalic acid chloride/121 as well as by DCC/HOBt/118 In the synthesis on solid support, longer coupling times are required when compared to N-protected proline.1[235 ... [Pg.78]

Synthesis of organic acids labelled with 125/ in pivalic acid melt... [Pg.1007]

Carboxylic mixed anhydrides are very important for the rapid synthesis of peptides by the stepwise procedure,however the use of carboxylic mixed anhydrides,e.g.those derived from pivalic acid and a protected amino acid (1),suffers from two disadvantages. Firstly,regiospecificity of attack at the desired carboxyl function is largely determined by steric effects and will not be 100% for all coupling reactions.Secondly,such mixed anhydrides have a propensity towards disproportionation to symmetric anhydrides which is highly undesirable in terms of reaction efficiency.This latter process can be depressed by operation of the reaction at -15 °C, but with the concurrent decrease in reaction rate and,on large scale manufacture,increased costs. [Pg.200]

In the original synthesis, there still remained three problems (a) conversion of the 3-iso compound into the 3-normal (b) replacement of the 18-0-acetate by a trimethoxybenzoyloxy group and (c) the resolution of the racemic alkaloid. The last two problems require no detailed comments, but the solution provided for the first led to the reserpine configuration, resulting in an unequivocal proof of the stereochemistry at C-3. The lactone of dCisoreserpic acid was prepared, and this, upon refluxing in pivalic acid, was converted into the thermodynamically... [Pg.316]

Figure 6.28 Synthesis of a chiral oxazolyl imidazolium salt from imidaolyl pivalic acid and (S)-valinol. Figure 6.28 Synthesis of a chiral oxazolyl imidazolium salt from imidaolyl pivalic acid and (S)-valinol.
Figure 3.6 Structures of (a) [DyL3(H20)3] and (b) [TbL lHiOja] (HL = pivalic acid and HE = 2, 6-dihydoxybenzoic acid) [RE, black O, grey C, white H, omitted]. (Redrawn from the CIF files of M.L. Huang et al, Study on the synthesis and the structures of rare earth complexes with 4-aminobenzoic acid, Huaxue Yanjiu Yu Yingyong (Chinese) (Chemical Research Applications), 18, 245-251, 2006 [30] and T. Glowiak et al., Crystal structure of the isomorphous complexes tetraaquabis(2,6-dihydroxy-benzoato-0)(2,6-dihydroxy-benzoato-0, O)terbium(III) and hohnium(III)dihydrate, Journal of Coordination Chemistry, 48 (4), 477-486, 1999 [43].)... Figure 3.6 Structures of (a) [DyL3(H20)3] and (b) [TbL lHiOja] (HL = pivalic acid and HE = 2, 6-dihydoxybenzoic acid) [RE, black O, grey C, white H, omitted]. (Redrawn from the CIF files of M.L. Huang et al, Study on the synthesis and the structures of rare earth complexes with 4-aminobenzoic acid, Huaxue Yanjiu Yu Yingyong (Chinese) (Chemical Research Applications), 18, 245-251, 2006 [30] and T. Glowiak et al., Crystal structure of the isomorphous complexes tetraaquabis(2,6-dihydroxy-benzoato-0)(2,6-dihydroxy-benzoato-0, O)terbium(III) and hohnium(III)dihydrate, Journal of Coordination Chemistry, 48 (4), 477-486, 1999 [43].)...
In peptide chemistry, activation with pivalic acid mixed anhydrides allows condensation with a-alkyl-a-amino acids (e.g. Aib), A -methyl-a-amino acids (resulting in the total synthesis of cyclosporin A) and Boc-Asn. ... [Pg.385]

For example, industrially, pivalic acid is prepared from CO and butene isomers at 80°C and 20-100 atm (Koch synthesis). ... [Pg.457]

Beilstein Handbook Reference) Acetic acid, trimethyl- AI3-04165 BRN 0969480 EINECS 200-922-5 HSDB 5211 Kyselina 2,2-dimethylpropionova Kyselina pivalova Neopentanoic acid NSC 65449 tert-Pentanoic acid Pivalic acid Propionic acid, 2,2-dimethyl- Trimethylacetic acid Versatic 5. Solid mp = 35" bp = 164" d = 0.905 soluble in H2O (2.5 g/100 ml), more soluble in EtOH, Et20. Lancaster Synthesis Co. Mallinckrodt Inc. Shiva Pharmachem Sigma-Aldrich Fine Chem. [Pg.502]

The first use of a polymer-supported Mukaiyama reagent for microwave-mediated synthesis of amides was presented in 2004 [125]. To prove its effectiveness, even in difficult coupling reactions, it was used in the microwave-accelerated synthesis of an amide from sterically hindered pivalic acid (Scheme 16.83). The mixture was subjected to microwave irradiation at 100 °C for 10 min and the desired product was obtained in 80% yield. [Pg.776]

The Paal-Knorr synthesis succeeds especially well in presence of one equivalent of pivalic acid, in a solvent mixture of toluene/heptane/THF at a ratio of 1 4 1. Deprotection and salt formation with calcium acetate finally yield ator-vastatin. [Pg.432]


See other pages where Pivalic acid synthesis is mentioned: [Pg.316]    [Pg.92]    [Pg.156]    [Pg.63]    [Pg.134]    [Pg.238]    [Pg.372]    [Pg.68]    [Pg.675]    [Pg.156]    [Pg.156]    [Pg.1307]    [Pg.1007]    [Pg.26]    [Pg.156]    [Pg.50]    [Pg.675]    [Pg.675]    [Pg.74]    [Pg.370]    [Pg.144]    [Pg.385]    [Pg.3146]    [Pg.238]    [Pg.123]    [Pg.47]    [Pg.83]   


SEARCH



Pival

Pivalate

Pivalates

Pivalic acid

© 2024 chempedia.info